The heat in industrial hot water or low pressure steam is frequently waste heat, since it cannot be efficiently utilized for heating, drying or chemical processes, or to produce mechanical or electrical energy. As well as being useless at the site of production, such hot water or water heated by the steam may pose a disposal problem, since direct flow into many streams or other bodies of water may provide thermal pollution.
The process described here may be used to concentrate a significant amount of this heat into water or steam, bringing it to a higher temperature, thus providing a source of useful heat and reducing the fuel requirements and heat disposal provisions for an industrial process. There are other systems, such as heat pumps, which can raise the temperature of some water while lowering the temperature of other water, but such systems require an input of mechanical energy or higher temperature heat; whereas the process here described requires only sufficient outside energy to transfer materials through the system and to instrument and control the transfers.
The process uses the exothermic conversion of substances A to substances B in a reaction chamber. The heat liberated in this conversion is added, via heat exchange, to a portion of the influent hot water, producing water at a higher temperature or steam which can be used as a source of useful energy. The substances B are separated from the mixture and, in another reaction chamber, converted back to A, absorbing heat which is furnished by another portion of the influent hot water. The net result of these steps is that a stream of hot water is separated into two streams, one hotter than the original stream, and one cooler.
In order for the described system to work, several conditions are necessary:
(1) In addition to the influent hot water, there must be at least one cooler influent stream (e.g. water or air) which gains heat from the process in such a way that the second law of thermodynamics is not challenged. In an isolated system, division of a body of intermediate temperature into a warmer body and a cooler body is attended by a decrease in entropy which is not permitted by the second law; but adequate heating of a still cooler body within the system can satisfy the law.
(2) At temperatures which may be held by available influent fluids, the equilibrium concentrations of both A and B substances in the reaction mixture must be substantial.
(3) A to B reaction speeds must be slow enough so that a minimum of reaction occurs during separation of B from A and during transfer to and from the reaction chambers; and A to B reaction speeds within the reaction chambers must be fast enough so that heat is released rapidly enough or absorbed rapidly enough to make the process practical. One method of accomplishing this is to utilize a normally slow reaction and to provide catalyst to speed the reaction in the reaction chambers.
As an example, the modification of a power plant using the process is described. Large, modern, steam power plants are designed for very high efficiency. The steam fed to the turbine is expanded through several stages, finally ending as a very low pressure vapor. This is condensed by cooling water; and the condensate is returned to the steam boiler. On its way, the condensate collects heat from the steam at several stages in the turbine and is reintroduced hot to the boiler.
However, there is an appreciable amount of the heat taken away by the cooling water which could be saved and redirected to some useful purpose, perhaps to reduce the fuel needed in the power plant operation or to increase the power produced or to serve as a heat source for some other process. How this may be done is explained with reference to the accompanying figures.